Corrosion-resistant impeller for a magnetic-drive centrifugal pump

ABSTRACT

An impeller for a magnetic-drive centrifugal pump includes a core for supporting a magnetic assembly of magnets. An inner barrier covers at least part of the magnets. The inner barrier hermetically isolates the magnetic assembly within the impeller. For example, in one embodiment the inner barrier may be sealed or hermetically connected to the core at one or more seams. An outer barrier overlies the inner barrier.

FIELD OF THE INVENTION

This invention relates to a corrosion-resistant impeller for amagnetic-drive centrifugal pump.

BACKGROUND

Magnetic-drive centrifugal pumps may be used to pump fluids, such ascaustic and hazardous liquids. Instead of shaft seals, a magnetic-drivepump features a pump shaft separated from a drive shaft by a containmentshell. The drive shaft is arranged to rotate with one magnetic assembly,which is magnetically coupled to another magnetic assembly. The magneticassemblies cooperate to apply torque to the pump shaft to pump a fluidcontained by the containment shell.

In a magnetic-drive centrifugal pump, the impeller is exposed to thepumped fluid. The magnetic assembly of the impeller may be encapsulateddirectly with a polymeric layer to protect the magnetic assembly fromoxidation or corrosion by the pumped fluid. However, the polymeric layeris generally semi-permeable or sufficiently permeable to allow some ofthe pumped fluid (or constituents) to migrate through the polymericlayer to the magnetic assembly. Over time, one or more magnets of themagnetic assembly may be oxidized or corroded from exposure to thepumped fluid. When rust or other deposits form on a magnet, theproperties of the magnet may change which may degrade performance of thepump in any of the following ways: (1) delamination of the polymericlayer from the magnet, (2) increased size of the magnet along withdecreased axial clearance between the impeller and the pump interior,and (3) reduction in the magnitude of the magnetic field produced by themagnets. If a decrease in axial clearance is great enough, rubbingcontact between the impeller and the pump interior may lead to failureof the pump. For example, the integrity of the containment shell may becompromised by mechanical scraping of the impeller or the pumped fluidmay be contaminated by chemical interaction with an exposed portion ofthe magnetic assembly. If the magnetic coupling force is reduced bydegradation of the impeller magnets, the pump may operate with reducedtorque and lower pumping capacity. Thus, a need exists for improving theprotection of the magnetic assembly of the impeller from the pumpedfluid.

SUMMARY

In accordance with one aspect of the invention, an impeller for amagnetic-drive centrifugal pump comprises a core. The core supports amagnetic assembly of magnets. An inner barrier covers at least part ofthe magnets. The inner barrier hermetically isolates the magneticassembly within the impeller. For example, in one embodiment the innerbarrier may be sealed or hermetically connected to the core at one ormore seams. An outer barrier overlies the inner barrier.

The outer barrier may vary in accordance with several possibleconfigurations. In one embodiment, the outer barrier encapsulates theinner barrier so that the magnetic assembly is protected from the pumpedfluid by a dual protective scheme. In another embodiment, the outerbarrier is perforated with one or more openings such that the outerbarrier at least partially encapsulates the inner barrier. If the outerbarrier is semi-permeable or somewhat permeable, the openings preventhydraulic pressure differentials from damaging or deforming the outerbarrier during transient pump operating conditions. Thecorrosion-resistant impeller provides a reliable protective barrier thatprevents or eliminates the ingress of pumped fluid that might otherwiseattack the magnetic assembly of the impeller. Accordingly, thereliability and longevity of a pump may be enhanced by incorporation ofthe impeller into a magnetic-drive centrifugal pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross section of a centrifugal magnetic-drive pump inaccordance with one embodiment of the invention.

FIG. 2 is a cross-sectional view of an impeller of the pump of FIG. 1.

FIG. 3 is an internal section of the impeller of FIG. 2 prior to theformation of an outer polymeric structure.

FIG. 4 is a flow chart of a method for making an impeller in accordancewith one embodiment of the invention.

FIG. 5 is a cross section of another embodiment of a centrifugalmagnetic-drive pump.

FIG. 6 is a cross-sectional view of an impeller of FIG. 4.

FIG. 7 is a cross section of another embodiment of a centrifugalmagnetic-drive pump having a thrust balancing system.

FIG. 8 is a cross-sectional view of an impeller of FIG. 7

FIG. 9 through FIG. 14, inclusive, are cross sections of variousalternate embodiments of impellers.

DETAILED DESCRIPTION

In accordance with one embodiment of the invention, FIG. 1 illustrates acentrifugal pump 10. The centrifugal pump 10 includes a housing 12, ashaft 30, a radial bearing 34, and an impeller 20. The housing 12 has ahousing cavity 14, an inlet 16, and an outlet 18. The housing 12 may becast, molded, or otherwise formed by a group of housing sections whichcan be connected by fasteners, adhesives, or both. The housing cavity 14is preferably lined with a corrosion-resistant material 44. A shaft 30is located in the housing cavity 14. A radial bearing 34 coaxiallysurrounds the shaft 30. The shaft 30 and the radial bearing 34 arerotatable with respect to one another.

An impeller 20 is positioned to receive fluid from the inlet 16 and toexhaust fluid to the outlet 18 during rotation of the impeller 20. Theimpeller 20 receives the radial bearing 34.

FIG. 1 illustrates one configuration of a magnetic-drive pump 10 inwhich the shaft 30 is cantilevered. The shaft 30 has a first end 52 anda second end 54. In this embodiment, the first end 52 mates with asocket 46 in a containment member 48 or is otherwise mechanicallysupported by the containment member 48. The second end 54 is locatednear a hub 49 of the impeller 20. The shaft 30 of FIG. 1 is generallyhollow or otherwise configured to reduce or eliminate the tendency ofhydraulic forces to pull the shaft 30 out from the socket 46 in thecontainment member 48.

Although the shaft 30 is cantilevered, hollow, and stationary as shownin FIG. 1, various other shaft configurations are possible and fallwithin the scope of the invention. In a first alternate configuration,the shaft 30 is supported at multiple points, rather than beingcantilevered. In a second alternate configuration, the shaft 30 issolid, instead of hollow. In a third alternate configuration, the shaft30 is configured to rotate with respect to the housing 12 and one ormore radial bearings associated with the shaft 30 may be stationary. Anyfeatures of the first, second and third alternate configurations may becombined to yield a solid shaft that rotates with respect to thehousing, for example.

The shaft 30 is preferably composed of a ceramic material or a ceramiccomposite. In an alternate embodiment, the shaft 30 is composed of astainless steel alloy or another alloy with comparable or superiorcorrosion-resistance and structural properties. In another alternateembodiment, the shaft 30 comprises a metal base coated with a ceramiccoating or another hard surface treatment.

A wear ring assembly (22, 24) may be associated with the front side 11of an impeller 20. The wear ring assembly (22, 24) includes a first wearring 22 and a second wear ring 24. The first wear ring 22 is associatedwith the impeller 20 and the second wear ring 24 is associated with thehousing 12 of the pump 10. The second wear ring 24 may be affixed to thehousing cavity 14. The first wear ring 22 may be retained by acorresponding retainer 26 and the second wear ring 24 may be retained bya respective retainer 28. In one embodiment, the wear ring assembly (22,24) may be composed of ceramic material because ceramic materials tendto hold their tolerances over their lifetime. In addition, smallertolerances and clearances are possible with ceramic wear rings than formany metals, alloys, polymers, plastics and other materials that arealso suitable for wear rings.

In one embodiment, the radial bearing 34 comprises a bushing 15 (e.g.,ceramic bushing or carbon bushing) housed in a bearing retainer 13. Forexample, the bushing 15 may be composed of a ceramic material, such assilicon carbide. In an alternative embodiment, the radial bearing maycomprise ceramic pads or carbon pads housed in a bearing retainer.

In one configuration, the radial bearing 34 is mated, interlocked, orotherwise mechanically joined with the impeller hub 49 to preferablydefine an opening (e.g., a series of spline-like openings) between theimpeller hub 49 and the exterior 17 of the radial bearing 34. Theopening allows pumped fluid to travel from the wear ring assembly (22,24) around the back side of the impeller 20 through the hub 49 and backto the suction chamber 19. The suction chamber 19 is defined by thevolume in the interior of the pump around the inlet 16 and the impellereye 80.

The impeller 20 preferably comprises a closed impeller, although inother embodiments open impellers, or partially closed impellers may beused. The impeller 20 includes a front side 11 facing the inlet 16 and aback side 21 opposite the front side 11. For a closed impeller 20 asshown in FIG. 1, the front side 11 may be a generally annular surfacethat terminates in a flange 23. The back side 21 may include a generallycylindrical portion 86 and a generally annular surface 87 extendingradially outward from the cylindrical portion 86. The impeller 20includes blades 78 for propelling fluid outward from an impeller eye 80(e.g., toward the outlet 18) during rotation of the impeller 20.

A first magnet assembly 38 is preferably associated with the impeller 20such that the first magnet assembly 38 and the impeller 20 rotatesimultaneously. The first magnet assembly 38 of magnets 36 may beintegrated into the impeller 20 as shown in FIG. 1A second magnetassembly 40 is carried by a rotor 42. A drive motor (not shown) iscapable of rotating the drive shaft 25 and the rotor 42. The secondmagnet assembly 40 is oriented in magnetic communication with respect tothe first magnet assembly 38. The magnetic assemblies (38, 40) supportmagnetic coupling between each other to permit the drive shaft 25 totransmit torque to the impeller 20 through the containment member 48.

The containment member 48 is oriented between the first magnet assembly38 and the second magnet assembly 40. The containment member 48 may besealed to the housing 12 to contain the pumped fluid within a wet-end 27of the pump and to isolate the wet-end from a dry-end 29 of the pump.

The containment member 48 is preferably made of a dielectric in theregion where the first magnetic assembly 38 and the second magneticassembly 40 face one another. For example, the containment member 48 maybe composed of one or more layers of a polymer, a plastic, areinforced-polymer, a reinforced plastic, a plastic composite, a polymercomposite, a ceramic, a ceramic composite, a reinforced ceramic or thelike. Multiple dielectric layers may be used to add structural strengthto the containment member 48 as illustrated in FIG. 1.

Although the containment member 48 includes a metallic reinforcement forstructured support of the shaft 30, an alternate embodiment may deletethe metallic reinforcement 48. Notwithstanding the foregoing compositionof the containment member 48, alternate embodiments may use metallicfibers to reinforce the dielectric, a metallic containment shell insteadof a dielectric one, or a single layer of dielectric instead of multiplelayers.

The wear ring assembly (22, 24) defines a boundary between a suctionchamber 19 and a discharge chamber 31 of the pump 10. A primary flowpath of the pumped fluid extends between the inlet 16 and an outlet 18of the pump. A secondary flow path of the pumped fluid extends from thegap between rings of the wear ring assembly (22, 24) to the impeller hub49 around the back 21 of the impeller 20. The second flow path isdefined by the region between the containment member 48 and the impeller20 and by the region between the impeller 20 and the shaft 30.

FIG. 2 shows an enlarged view of the impeller 20 of FIG. 1. Likereference numbers in FIG. 1, FIG. 2, and FIG. 3 indicate like elements.The impeller 20 for a magnetic-drive centrifugal pump (e.g., pump 10)includes a core 58. The core 58 supports the first magnet assembly 38.The magnets 36 of the first magnet assembly 38 are mounted about aperiphery of the core 58. The core 58 may be composed of metallicmaterial (e.g., a ferrous alloy or metal). An inner barrier 50, forfluidic isolation of the first magnetic assembly 38 from the pumpedfluid, covers at least part of the magnets 36. The inner barrier 50 issealed or hermetically connected (e.g., welded) to the core 58 at one ormore seams (e.g., a first seam 64). Hermetically connected or sealedmeans that the inner barrier 50 is sealed to another part of theimpeller (e.g., impeller 20) by welding, fusion, soldering, brazing, oranother bonding technique to prevent fluid (e.g., the pumped fluid),liquid, gas, or air from traversing the inner barrier 50 into itsinterior volume. The magnets 36 are disposed in the interior volumebetween the inner barrier 50 and the core 58. An outer barrier 56overlies the inner barrier 50. In this embodiment, the outer barrier 56encapsulates the inner barrier 50 and the first magnetic assembly 38 isprotected from the pumped fluid by two protective layers. The outerbarrier 56 preferably surrounds the inner barrier 50 and at least aportion of the core 58. Although the outer barrier 56 preferablycomprises a polymeric layer and the inner barrier 50 comprises ametallic barrier or shield, other materials may be used for the innerbarrier 50 and the outer barrier 56.

In one embodiment, the core 58 has a generally cylindrical exteriorsurface 92 and a generally cylindrical interior surface 90. The magnets36 are spaced apart in a loop around the cylindrical exterior surface 92of the core 58. The spatial volume between the magnets 36 may definecavities within the impeller 20. The cavities may be referred tocollectively as the interior volume. The cylindrical exterior surface 92may have a step 96 or another feature to facilitate proper alignment ofthe magnets 36 at radial intervals about the generally cylindricalexterior surface 92. In one embodiment, a sleeve 70 may engage at leasta portion of the cylindrical exterior surface 92 of the core 58. Thesleeve 70 may be composed of a metallic material (e.g., a non-ferrousalloy or metal). In one embodiment, the cylindrical interior surface 90may have channels 94 (e.g., generally annular channels) or anothersurface variation to promote adhesion of the outer barrier 56 to thecylindrical interior surface 90 of the core 58.

In an alternate embodiment, the channels 94 may be deleted so that thatcylindrical interior surface 90 is curved and generally cylindrical.

The inner barrier 50 hermetically isolates the first magnetic assembly38 from any pumped fluid that might otherwise traverse or permeate theouter barrier 56. Hermetic isolation means that the inner barrier 50 isairtight, liquid-tight, or both. The hermetic isolation is provided by ahermetic connection or seal that is generally resistant to chemical andphysical properties of the pumped fluid to keep the magnets 36 of thefirst magnetic assembly 38 dry and free of pumped fluid.

The inner barrier 50 forms at least one wall of a container thatcontains the magnets 36. Another part of the impeller may formadditional walls of the container for containing the magnets 36. Asshown in FIG. 2, the inner barrier 50 may have a generally hollowcylindrical shape that terminates in a generally orthogonal angle at oneend. Accordingly, the inner barrier 50 may be shaped like a generallycylindrical cup with a hole in its bottom and without a handle.

The inner barrier 50 may be formed in any of the following illustrativetechniques. In accordance with a first construction technique, the innerbarrier 50 may be stamped from metallic sheet stock. In accordance witha second technique, the inner barrier 50 may be formed from an extrudedcylindrical portion with an end ring attached (e.g., welded) to one endof the cylindrical portion. In accordance with a third technique, theinner barrier 50 may be formed of sheet stock that is rolled and weldedalong a longitudinal seam to form a cylindrical portion. An end ring orwasher is attached (e.g., welded) to one end of the cylindrical portionto form the inner barrier 50. Other techniques for forming the innerbarrier 50 might include casting, bending, machining or othermetallurgical fabrication processes.

The inner barrier 50 has a first end 52 and a second end 54. The firstend 52 of the inner barrier 50 adjoins a core rear 60 of the core 58.The first end 52 of the inner barrier 50 is sealed or hermeticallyconnected (e.g., welded) to the core 58 at a first seam 64. The firstseam 64 is indicated by the dashed circle associate with referencenumeral 64. In the configuration of FIG. 2, the sleeve 70 has a step 72or a channel that engages a second end 54 of the inner barrier 50,although other joint configurations are possible (e.g., butt joint andlap joint). The second end 54 of the inner barrier 50 is sealed orhermetically connected (e.g., welded) to the sleeve 70 at a second seam66. The second seam 66 is indicated by a dashed circle associated withthe reference numeral 66.

In the embodiment of FIG. 1, FIG. 2 and FIG. 3, the impeller 20 hasthree seams that are sealed with respect to fluid or hermeticallyinterconnected. The first seam 64 is located at the junction of theinner barrier 50 and the core 58. In the embodiment of FIG. 1, FIG. 2and FIG. 3, the first seam 64 is disposed near or at the core rear 60;the first seam 64 follows a generally circular path around a rear 35(FIG. 3) of the internal impeller section 33 (FIG. 3). The second seam66 is located near or at the junction of the inner barrier 50 and thesleeve 70. The second seam 66 follows a generally annular path around acylindrical portion 86 of the impeller 20. A third seam 68 is located atthe junction of the core 58 and the sleeve 70. In the embodiment of FIG.1, FIG. 2, and FIG. 3, the third seam 68 is disposed at or near a front37 (FIG. 3) of the internal impeller section 33 (FIG. 3); the third seam68 follows a generally annular path around a front 37 of the internalimpeller section 33.

The sealing or hermetic interconnection of each seam may be madeaccording to several different techniques. Under a first technique, thesealing or hermetic interconnection is made by welding adjoiningmetallic components or by fusing adjoining metallic components with theapplication of heat, pressure, or both. Under a second technique, thesealing or hermetic interconnection is made by brazing adjoiningmetallic components. Under a third technique, the sealing or hermeticinterconnection is made by soldering adjoining metallic components.Advantageously, the hermetic interconnection of the first through thethird techniques may be formed of non-permeable materials (e.g., metalsor alloys) that prevent the flow or passage of the pumped fluid or anygas within the pumped fluid through the hermetic interconnection. Thehermetic interconnection of the first through the third techniques isnot formed of semi-permeable materials (e.g., adhesives, elastomers orpolymers) that may allow diffusion or penetration of the pumped fluid orconstituent components (e.g., any gas, solvent, or volatile organiccompound) of the pumped fluid. Under a fourth technique, the sealing orhermetic interconnection is made by a mechanical fasteners (e.g., rivotsor threads) or a mechanical connection (e.g., a snap-fit connector).Under a fifth technique, the sealing or hermetic interconnection is madeby a seal (e.g., a gasket, an elastomeric member, or an elastomericO-ring) that adjoins adjacent components of similar or differentcomposition. The seal cooperates with mechanical connection that fastensor secures adjacent components of similar or different composition.Under a seventh technique, the third seam may be formed by a compressivefit between the sleeve and the core, a threaded connection between thesleeve and the core, by a seal, or any combination of the foregoingitems.

The first, second, and third seams (64, 66 and 68) provide isolation(e.g., hermetic isolation) of the magnets 36 (e.g., the first magneticassembly 38) from the deleterious effects of exposure to pumped fluid.In particular, the inner barrier 50, the core 58 the sleeve 70, andtheir associated seams (64, 66, and 68) cooperate to form an innerprotective container for preventing the oxidation and corrosion of themagnets 36 (e.g., the first magnetic assembly 38) within the impeller20. The inner protective container represents a hermetically sealedchamber for protection of the first magnetic assembly 38.

In one or more embodiments, the volume around the magnets 36 of theimpeller 20 may be filled with a filler 75 (e.g., a corrosion-inhibitingfiller or a polymer) via a bore 74 in sleeve 70. The bore 74 may besealed with a corresponding cap 76.

In an alternate embodiment, the volume around the magnets 36 may beconfigured as an air cavity that is not filled with a filler 75 andcapped with cap 76, where the air cavity is consistent with themanufacturing techniques employed in fabrication of the impeller.

The outer barrier 56 overlies the inner barrier 50 and may encapsulatethe entire internal impeller section 33 to form an outer protectivecontainer. The outer protective container may prevent or inhibitoxidation or corrosion of the magnets 36 of the impeller 20. The outerprotective container protects the inner protective container and themagnets 36 from the pumped fluid. Even if the pumped fluid breaches theouter protective container, the inner protective container prevents thepumped fluid from contacting, corroding, or chemically attacking thefirst magnet assembly 38. Together, the inner protective container andthe outer protective container provide a highly reliable, dualprotection against the ingress of pumped fluid that might otherwisechemically attack or corrode the magnets 36. Accordingly, the impeller(e.g., impeller 20 of FIG. 2) has at least two protective containers toprotect the first magnet assembly 38 from the physical and chemicalproperties of the pumped fluid.

In one embodiment, the outer barrier 56 may be composed of polymer(e.g., a corrosion-resistant polymer). Suitable corrosion-resistantpolymers for the outer barrier 56 include epoxy and vinyl ester resin,for example. FIG. 3 shows an internal section of the impeller 20 priorto formation of the outer barrier 56. FIG. 2 shows the impeller 20 afterthe formation of the outer barrier 56 of a polymer.

In an alternate embodiment, the outer barrier 56 is composed of apolymeric matrix and a reinforcing material distributed within thepolymeric matrix. For example, the outer layer may be composed of apolymer composite, a plastic composite, a fiber-reinforced plastic, afiber-reinforced polymer, carbon fiber-filled polytetrafluoroethylene(PTFE), or another structurally suitable composition. The polymericmatrix may comprise a polymer or plastic, such as PTFE or ethylenetetrafluoroethylene (ETFE). The reinforcing material may comprise carbonfiber, ceramic, metal fiber, glass fiber, or another suitablestructural-enhancing filler.

The inner barrier 50, the core 58, and the sleeve 70 may be constructedof a corrosion-resistant metal, a corrosion-resistant alloy, or anymetal or alloy that is compatible with or resistant to corrosion orunwanted chemical reaction with the pumped fluid. In one embodiment, theinner barrier 50, the core 58 and the sleeve 70 are preferablyconstructed from the substantially similar metals or alloys tofacilitate welding, fusing, or brazing of the inner barrier 50, the core58 and the sleeve 70 at the first seam 64, the second seam 66 and thethird seam 68. Use of the same or substantially similar metals or alloysfor the inner barrier 50, the core 58, and sleeve 70 may serve tomaximize the compatibility of the impeller 20 with a wide assortment ofpumped fluids. For example, the core 58, the sleeve 70, and the innerbarrier 50 may be composed of stainless steel.

In one embodiment, the inner barrier 50 is composed of 304L low carbonstainless steel or 316 low carbon stainless steel. When 304L stainlessor 316 stainless steel are welded less carbides are formed than withsome other stainless alloys. Carbides are less corrosion resistant thanthe stainless steel itself.

In an alternate embodiment, the core 58, the inner barrier 50, or bothmay be composed of HASTELLOY for corrosion resistance to a particularpumped fluid. HASTELLOY metal alloy is a registered trademark of HaynesInternational, Inc. of Kokomo, Ind.

In another alternate embodiment, the core 58 is composed of carbonsteel, ductile iron, or another ferrous alloy to provide a desired levelof torque transfer between the first magnet assembly 38 and the secondmagnet assembly 40.

FIG. 3 illustrates the internal impeller section 33. The internalimpeller section 33 has a font side 37 and a back side 35. Likereference numerals in FIG. 1, FIG. 2, and FIG. 3 indicate like elements.

FIG. 4 is a flow chart of a method for fabricating an embodiment of animpeller (e.g., impeller 20) in accordance with the invention. Themethod of FIG. 4 begins in step S10.

In step S10, the inner barrier 50 is sealed or hermetically connected toan internal impeller section (e.g., internal impeller section 33) at oneor more seams. The internal impeller section 33 may have any number ofseams that are necessary to form an inner protective container for themagnets 36. The number of seams vary in accordance with severalalternate embodiments. In a first embodiment, the inner barrier 50 issealed or hermetically connected to the core 56 at the first seam 64;the inner barrier 50 is sealed or hermetically connected to the sleeve70 at the second seam 66; and the sleeve 70 is sealed or hermeticallyconnected to the core 58 at the third seam 68.

In a second embodiment, only two seams are present if the core and thesleeve are integrated into a single unit. The single unit may bereferred to as a unitary core which replaces the core 56 and the sleeve70. Accordingly, the inner barrier 50 is sealed or hermeticallyconnected to the unitary core at a first seam and the inner barrier 50is sealed or hermetically connected to the core at a secondary seam(e.g., secondary seam 166 of FIG. 9 or FIG. 10). Although welding orfusion is preferably used to form the seal or hermetic connection of theseams (e.g., the first seam 64, the second seam 66, and the third seam68), other techniques may be used to form the seal or hermeticconnection of the seams.

Welding is generally preferred to brazing so as to reduce the number ofmetallic compounds used in the pump to prevent unwanted chemicalinteraction with a wide array of pumped fluids or specific pumpedfluids. Suitable welding techniques include, but are not limited to,laser welding and gas-tungsten-arc welding. Laser welding can becompleted in the presence of the magnets 36 and the quality of the weldis not generally affected by the magnetic field. Because laser weldingis susceptible to contamination on the surfaces to be welded, thesurfaces should be cleaned by a solvent, a detergent, or otherwisemechanically scrubbed prior to laser welding. Gas-tungsten-arc weldingprovides a highly localized heat source that prevents damage to themagnets 36.

In step S12, after welding or other heat is applied to form the seal orhermetic connection of the inner barrier 50, filler 75 (e.g., acorrosion inhibitor or a corrosion-resistant filler) may be introducedinto the spatial volume or cavities between the magnets 36 of theinternal impeller section 33. For example, filler 75 may be injected,poured, or otherwise introduced into the spatial volume or cavitiesbetween the magnets 36 of the first magnetic assembly 38 via one or morebores 74 in the sleeve 70. The filler 75 inhibits or prevents corrosionof the magnets 36 in the first magnetic assembly 38. The bore 74 may befilled with the filler 75 and optionally capped with a plug 76. In oneembodiment, the bore 74 and the plug 76 have corresponding threadsadapted for rotational engagement. The internal impeller section 33 isillustrated in FIG. 3 after the bore 74 is filled with filler 75 andcapped with a plug 76.

In an alternate embodiment, the plugs and the respective bores may notbe threaded (e.g., a press-fit may be used instead).

The filler may be used to protect the magnets 36 from oxidation andcorrosion from moisture or pumped fluid that somehow traverses otherprotective barriers to the magnets 36 within the impeller (e.g.,impeller 20). After hardening or containment, the filler 75 (e.g.,hardened or cross-linked polymeric filler) prevents the inner barrier 50from being crushed if the exterior of the impeller (e.g., impeller 20)is formed by injection molding over the internal impeller section 33.Injection molding includes compression molding, injection-compressionmolding, and other related techniques.

If the corrosion-resistant filler comprises a polymeric material, thefiller may be composed of one or more of the following: an elastomer, apotting compound, an epoxy, silicone, or a thermoset plastic. The fillerpreferably has an uncured liquid state that supports pouring, injectionor forced injection of the filler into cavities or other hollow volumeswithin the impeller (e.g., impeller 20) or internal impeller section 33.For example, thermoset plastic may be poured and later hardens bycross-linking.

In step S14, an outer barrier 56 and a remainder of the impeller ismolded over the internal impeller section 33 of FIG. 3 to form theremainder of the impeller (e.g., impeller 20). For example, theresultant impeller 20 of FIG. 2 may be formed by molding over theinternal impeller section 33 of FIG. 3. The remainder of the impeller 20includes the impeller blades 78, impeller eye 80, and hub 49, and recessin flange 23 for the first wear ring 22. In FIG. 2, the polymericstructure adjacent to the front side 37 (FIG. 3) of the internalimpeller section 33 (FIG. 3) represents a front portion of the outerbarrier 56 or the remainder of the impeller 20. FIG. 2 illustrates theinternal impeller section 33 plus the remainder of the impeller 20.Although FIG. 2 shows a closed impeller, other impeller configurationsare possible, such as an open or partially closed impeller.

The outer barrier 56 of the impeller 20 and the remainder of theimpeller 20 is preferably composed of a polymer. For example, the outerbarrier 56 may be composed of a fluoro-polymer, such as TEFZEL, afluorine-containing polymer. TEFZEL is a registered trademark of E. I.Du Pont de Nemours and Company of Wilmington, Del.

Step S14 is preferably carried out by a high-pressure molding process,injection molding, injection-compression molding, or compressionmolding. However, under an alternate procedure, the exterior of theimpeller 20 may be formed by lower pressure techniques in step S14, suchas resin-transfer molding or fiberglass molding techniques. Accordingly,if low-pressure molding techniques are used, the introduction of thefiller 75 in step S12 is not required for structural support during themolding of step S14, but may still be used to inhibit or preventcorrosion of the magnets 36.

In one example of a low-pressure molding technique, a drive assembly ofan impeller is inserted into a preformed section of the impeller thatmay be molded in accordance with any suitable technique. For instance,the drive assembly or impeller interior portion 33 of FIG. 3 may be slidinto a pocket that forms a remainder of the impeller 20 of FIG. 2,except for an opening. The opening may be closed by the formation of apolymeric cap (e.g., thermal processing or welding of a polymeric caponto the pocket at the rear of the impeller 20). The combination pocketand the polymer cap hermetically seals the internal impeller 20 assemblywithin a polymeric shell.

FIG. 5 shows an alternate embodiment of a pump 110 with an alternateimpeller 120. The pump of FIG. 5 is similar to the pump of FIG. 1 exceptthe impeller 120 of FIG. 5 features openings 44 in the outer barrier156. Like reference numbers in FIG. 1 and FIG. 5 indicate like elements.

In the embodiment of FIG. 5, if the outer barrier 156 is sufficientlyperforated with one or more openings 44, the pumped fluid readily exitsfrom the interior of the outer barrier 156 when the impeller 120 stopsrotating. The pumped fluid might otherwise be trapped in the interior ofthe outer barrier 156 in a manner that deforms the outer barrier 156 ifthe outer barrier 156 is permeable or semi-permeable (e.g., certainpolymers are permeable and semi-permeable). When the impeller 120 stopsrotating, the hydraulic pressure of the fluid around the impeller 120decreases, while the hydraulic forces experienced by the outer barrier156 readily decrease to equilibrium through venting of the openings 44in the outer barrier 156. Accordingly, the openings 44 reduce or preventthe formation any hydraulic pressure gradient within an outer barrier156 that is not impermeable. The prevention of the formation of thehydraulic pressure gradients prevents delamination of the outer barrier156 and deformation or bulging of the outer barrier 156. The openings 44may relieve pressure that might otherwise build up between the innerinternal impeller section 33 and the outer barrier 156. Theconfiguration of the pump 110 of FIG. 5 is well suited for operatingunder transient (e.g., stopping and starting) or high-pressureconditions.

FIG. 6 shows an enlarged version of the impeller 120 of FIG. 5. Theimpeller 120 features openings 44 in the outer barrier 156 as previouslydescribed in conjunction with FIG. 5. The impeller 120 of FIG. 6 issimilar to the impeller 20 of FIG. 2 except for the openings 44. Likereference numbers in FIG. 2 and FIG. 6 indicate like elements.

FIG. 7 shows a pump 210 having a thrust balancing system andincorporating an embodiment of a corrosion-resistant impeller 220. Theimpeller of FIG. 7 is similar to the impeller of FIG. 1 except for theflange 291 for the rear wear ring assembly 289 and impeller hub 277 thataccommodates ring 283. Like reference numbers indicate like elements inFIG. 1 and FIG. 7.

The impeller 220 includes an impeller hub 277 with an opening 279 and animpeller recess for receiving the radial bearing 34. A thrust balancingvalve 281 comprises a combination of a ring 283 and an end 285 of theshaft 30. The thrust balancing valve 281 is associated with the hub 277to define a variable orifice for fluidic communication between asecondary flow path 287 and the inlet 16. The pump 220 preferablyincludes a front wear ring assembly (222, 224) and a rear wear ringassembly (289) with axially extended rings which permit the thrustbalancing system to operate at an axial position within a range of axialpositions, based upon the operating point of the pump 220 and thespecific gravity of the pumped fluid. The range of axial positions mayrange between a forward limit and a rear limit. At the forward limit thefirst wear ring 222 contacts a thrust bearing 295. At the rear limit theshaft end 285 contacts the thrust balancing ring 283 of the variableorifice. The containment member 148 has a flange for supporting the rearwear ring assembly 289.

FIG. 8 shows an enlarged version of the impeller 220 of FIG. 7. Theimpeller 220 of FIG. 8 is similar to the impeller 20 of FIG. 2 exceptthe impeller 220 of FIG. 8 includes the impeller hub 277 and a flange291 for supporting a rear wear ring of the wear ring assembly 289. Theflange 291 has a recess 293 for accepting a retainer for retaining arear wear ring. Like reference numbers in FIG. 2 and FIG. 8 representlike elements.

FIG. 9 shows a cross section of an alternate embodiment of an impeller320. The impeller 320 of FIG. 9 is similar to the impeller 20 of FIG. 2except the impeller 320 of FIG. 9 has a unitary core 158 that replacesthe core 58 and the sleeve 70 of FIG. 2. Further, the impeller 320 ofFIG. 9 does not have the third seam. The first seam is located at a rearportion of the unitary core 158. A secondary seam 166 is located at acentral portion of the unitary core 158. The secondary seam 166 refersto a hermetic connection or seal between the inner barrier 50 and theunitary core 158. Like reference numbers in FIG. 2 and FIG. 9 indicatelike elements. The impeller 320 of FIG. 9 may be incorporated into anyembodiment of the pump described herein.

FIG. 10 shows a cross section of another embodiment of the impeller 420.The impeller 420 of FIG. 10 is similar to the impeller 320 of FIG. 9except the impeller 420 of FIG. 10 features an outer barrier 156 withopenings 44. The operation of the openings 44 was previously describedin conjunction with FIG. 5. Like reference numbers in FIG. 6 FIG. 9 andFIG. 10 indicate like elements. The impeller 420 may be incorporatedinto any embodiment of the pump described herein.

FIG. 11 shows a cross section of an additional embodiment of an impeller520. The impeller 520 of FIG. 11 is similar to the impeller 20 of FIG. 2except the impeller 520 features an inner barrier 150 and sleeve 170 ofdifferent configuration than the barrier 50 and the sleeve 70. Inparticular, the inner barrier 150 has a solid annular portion 151 and agenerally cylindrical tongue 153. The sleeve 170 is generally annularand has a recess 155 for engaging the cylindrical tongue 153. Likereference numbers in FIG. 2 and FIG. 11 indicate like elements.

A first seam 264 is located at a junction between the core 258 and theinner barrier 150. The core 258 and the inner barrier 150 arehermetically connected or sealed to one another at the first seam 264. Asecond seam 266 is located at junction between the inner barrier 150 andthe sleeve 170. The inner barrier 150 and the sleeve 170 arehermetically connected or sealed to one another at the second seam 266.A third seam is 268 is located at a junction between the sleeve 170 andthe core 258. The sleeve 170 and the core 258 are hermetically connectedor sealed to one another at the third seam 268 he seams (264, 266 and268) form a inner protective container about the magnet assembly 38 toprotect the magnet assembly 38 from damage from the pumped fluid or anygas within the pumped fluid. The impeller 520 may be incorporated intoany embodiment of the pump described herein.

FIG. 12 shows a cross section of an additional embodiment of an impeller620. The impeller 620 of FIG. 12 is similar to the impeller 520 of FIG.11 except the inner barrier 150 and the sleeve 170 are flipped end forend. Like reference numbers in FIG. 11 and FIG. 12 indicate likeelements. In FIG. 12 the inner barrier 150 is located toward a front ofthe impeller 620, whereas in FIG. 11 the inner barrier 150 was locatedtoward a rear of the impeller 520. Similarly, in FIG. 12 the sleeve 170is located toward a rear of the impeller 630, while in FIG. 11 thesleeve 170 is located toward a front of the impeller 520. The threeseams (264, 266, and 268) of FIG. 12 hermetically connect the innerbarrier 150, the sleeve 170, and the core 258 to protect the magnetassembly from the pumped fluid or any gas within the pumped fluid. Theimpeller 620 may be incorporated into any embodiment of the pumpdescribed herein.

FIG. 13 illustrates a cross section of an alternate embodiment of animpeller 720. The impeller 720 of FIG. 13 is similar to the impeller 520of FIG. 11 except the impeller 720 of FIG. 13 features a unitary core358 that replaces the combination of the sleeve 170 and the core 258 ofFIG. 11. Further, the impeller of FIG. 13 has two seams, instead of thethree seams of FIG. 11. The first seam 264 is disposed between theunitary core 358 and the inner barrier 150. The secondary seam 266 isdisposed between the unitary core 358 and the inner barrier 358. Thecombination of the unitary core 358, the inner barrier 150, the firstseam 264 and the secondary seam 266 form an inner containment member forprotection of the magnet assembly 38 from the pumped fluid or any gaswithin the pumped fluid. Like reference numbers represent like elementsin FIG. 11 and FIG. 13. The impeller 720 may be incorporated into anyembodiment of the pump described herein.

FIG. 14 shows a cross section of an alternate embodiment of an impeller820. The impeller 820 of FIG. 14 is similar to the impeller 220 of FIG.8 except the inner barrier 250 and the unitary core 458 have differentconfigurations and are joined by a mechanical connector. Like elementsin FIG. 14 and FIG. 8 are indicated by like reference numbers. The innerbarrier 250 and the unitary core 458 of FIG. 14 are configured withseals 459 (e.g., elastomeric o-rings) and a mechanical connector 461(e.g., a snap-fit connector) to provide two sealed interconnectionsbetween the inner barrier 250 and the unitary core 458. The innerbarrier 250, the unitary core 458, the mechanical connector 461 and theseals 459 cooperate to form an inner protective layer that protects themagnetic assembly 38 from the pumped fluid or gases within the pumpedfluid. The impeller 820 of FIG. 14 may be constructed without welding,brazing, soldering or heating of the magnets 36 to avoid thermal damageto the magnets 36 that might otherwise occur if improper fabricationtechniques were used. However, welded seams or other generallynon-permeable seams of the other embodiments of the impeller arepreferred to seals 459 because elastomeric or polymeric seals may besomewhat permeable to certain fluids or gases within the pump. Incontrast to most other embodiments disclosed herein, the permeability ofthe elastomers or polymers of the seals 459 may allow some pumped fluidor gases to traverse an inner protective layer of the configuration ofFIG. 14. The impeller 820 of FIG. 14 may be incorporated into any pumpdisclosed herein.

In FIGS. 2, 3, 6, 8, 9, 10, 11, 12, and 13 the general location ofvarious seams (e.g., the first seam, the second seam and the third seam)is indicated by dashed circles. Although the boundaries betweenadjoining components (e.g., inner barrier 50 and core 58) of the seamsare show as lines in the foregoing figures, in practice the boundariesmay become merged by heat, welding, fusion, or other techniques forjoining the adjoining components. It is understood that the figures areprovided for illustrative purposes and do not show fused or merged seamsto avoid confusion. Nevertheless, any of the seams in any of thedrawings may be merged or fused and fall within the scope of theinvention.

The above detailed description is provided in sufficient detail to allowone of ordinary skill in the art to make and use the invention. Theabove detailed description describes several embodiments of theinvention. The invention may have additional physical variations oradditional embodiments that are encompassed within the scope of theclaims. For example, the filler 75, the cap 76 and the channels 94 maybe deleted from any of the embodiments disclosed herein while fallingwithin the scope of the claims. Further, the first magnetic assembly 38may be formed of one or more magnets, because one magnet can bemagnetized with a series of different magnetic poles (e.g., multiplenorth and south poles). Accordingly, any narrow description of theelements in the specification should be used for general guidance ratherthan to restrict the broader descriptions of the elements in thefollowing claims.

1. A centrifugal pump comprising: a housing having a housing cavity, an inlet, and an outlet; a shaft located within the housing cavity; a radial bearing coaxially surrounding said shaft, the shaft and the radial bearing being rotatable with respect to one another; and an impeller positioned to receive a fluid from the inlet and to exhaust a fluid to the outlet, the impeller having an inner barrier covering and hermetically isolating a magnetic assembly within the impeller, an outer barrier overlying the inner barrier; the inner barrier composed of a metallic material and the outer barrier composed of a polymeric material.
 2. The centrifugal pump according to claim 1 wherein the impeller comprises a core, the inner barrier being hermetically connected to a core at a first seam.
 3. The centrifugal pump according to claim 2 wherein the impeller further comprises a sleeve, the inner barrier being hermetically connected to the sleeve at a second seam and the core and the sleeve being hermetically connected at a third seam.
 4. The centrifugal pump according to claim 1 wherein the impeller comprises a unitary core, the inner barrier hermetically connected to the unitary core at a first seam and a secondary seam.
 5. The centrifugal pump according to claim 1 wherein the outer barrier encapsulates the inner barrier, the outer barrier composed of a corrosion-resistant polymer and the inner barrier composed of corrosion-resistant, metallic material.
 6. The centrifugal pump according to claim 1 wherein a chamber is formed by the inner barrier and the core, the chamber containing magnets of the magnetic assembly, cavities between the magnets being filled with a filler.
 7. The centrifugal pump according to claim 6 wherein a volume of the cavities around the magnet assembly is filled with a corrosion-inhibiting filler.
 8. The centrifugal pump according to claim 1 wherein the outer barrier has radially extending openings that extend from an outer surface of the outer barrier and penetrate through the outer barrier.
 9. The centrifugal pump according to claim 1 wherein the impeller comprises a core and a sleeve, the inner barrier welded to a core at a first seam, the inner barrier welded to the sleeve at a second seam, and the core and the sleeve welded at a third seam.
 10. The centrifugal pump according to claim 1 wherein the impeller comprises a unitary core, the inner barrier welded to the unitary core at a first seam and a secondary seam.
 11. The centrifugal pump according to claim 1 further comprising a core and generally annular sleeve, the inner barrier having a generally solid annular portion and a tongue for engaging a recess in the sleeve, the core and the inner barrier hermetically connected at a first seam, the inner barrier and the sleeve hermetically connected at a second seam, the sleeve and the core hermetically connected at a third seam.
 12. The centrifugal pump according to claim 1 further comprising a unitary core that engages the inner barrier, the inner barrier having a generally solid annular portion and a tongue for engaging a recess in the unitary core, the inner barrier hermetically connected to the unitary core at a first seam and a secondary seam to protect the magnetic assembly.
 13. The centrifugal pump according to claim 1 further comprising a unitary core that engages the inner barrier at a mechanical connector, the unitary core and the inner barrier having joints with corresponding seals for isolating the magnetic assembly from pumped fluid.
 14. The centrifugal pump according to claim 1 wherein the inner barrier comprises a generally cylindrical portion welded to a ring at one end of the cylindrical portion.
 15. An impeller for a centrifugal pump comprising: a magnetic assembly comprising a plurality of magnets; a core for supporting the magnetic assembly; an inner barrier covering at least part of the magnetic assembly and hermetically connected to the core at one or more seams to provide a seal for a fluid; and an outer barrier overlying the inner barrier and surrounding at least part of the core.
 16. The impeller according to claim 15 wherein the inner barrier is composed of a metallic material and wherein the outer barrier is composed of a polymeric material.
 17. The impeller according to claim 15 wherein the inner barrier is hermetically connected to the core at a first seam.
 18. The impeller according to claim 17 further comprising a sleeve, the inner barrier being hermetically connected to the sleeve at a second seam, the core and sleeve being hermetically connected at a third seam.
 19. The impeller according to claim 15 wherein the inner barrier is hermetically connected to a core at a first seam and a secondary seam.
 20. The impeller according to claim 15 wherein the inner barrier is welded to the core at a first weld seam and a second weld seam.
 21. The impeller according to claim 15 wherein the outer barrier encapsulates the inner barrier, the inner barrier composed of a corrosion-resistant polymer and the inner barrier composed of a corrosion-resistant metallic material.
 22. The impeller according to claim 15 wherein a chamber is formed between the inner barrier and the core, the magnetic assembly having magnets disposed within the chamber, cavities between the magnets filled with a filler.
 23. The impeller according to claim 15 further comprising a sleeve adjoining the core, the sleeve being welded to the core.
 24. The impeller according to claim 15 wherein the outer barrier has radially extending holes that extend from an outer surface of the outer barrier and penetrate through the outer barrier.
 25. The impeller according to claim 15 further comprising a sleeve, the inner barrier welded to a core at a first seam, the inner barrier welded to the sleeve at a second seam, and the core and the sleeve welded at a third seam.
 26. The centrifugal pump according to claim 15 wherein the inner barrier is welded to the core at a first seam and a secondary seam.
 27. The impeller according to claim 15 further comprising a generally annular sleeve, the inner barrier having a generally solid annular portion and a tongue for engaging a recess in the sleeve, the core and the inner barrier hermetically connected at a first seam, the inner barrier and the sleeve hermetically connected at a second seam, the sleeve and the core hermetically connected at a third seam.
 28. The impeller according to claim 15 wherein the inner barrier has a generally solid annular portion and a tongue for engaging a recess in the core, the inner barrier hermetically connected to the core at a first seam and a secondary seam to protect the magnetic assembly.
 29. The impeller according to claim 15 further comprising a mechanical connector associated with the inner barrier and the core, the mechanical connector interconnecting the inner barrier and the core, the core and the inner barrier having joints with corresponding seals for isolating the magnetic assembly from pumped fluid.
 30. The impeller according to claim 15 wherein the inner barrier comprises a generally cylindrical portion welded to a ring at one end of the cylindrical portion.
 31. A centrifugal pump comprising: a housing having a housing cavity, an inlet, and an outlet; a shaft located within the housing cavity; a radial bearing coaxially surrounding said shaft, the shaft and the radial bearing being rotatable with respect to one another; and an impeller positioned to receive a fluid from the inlet and to exhaust a fluid to the outlet, the impeller having an inner barrier covering and hermetically isolating a magnetic assembly within the impeller, an outer barrier overlying the inner barrier, the inner barrier having a hermetic interconnection associated with a corresponding seam, the hermetic interconnection comprising a nonpermeable metallic material.
 32. The centrifugal pump according to claim 31 wherein the nonpermeable metallic material is selected from the group consisting of a metal and an alloy.
 33. The centrifugal pump according to claim 31 wherein the nonpermeable metallic material comprises solder associated with soldering of the inner barrier to an adjoining metal component of the impeller.
 34. The centrifugal pump according to claim 31 wherein the hermetic interconnection further comprises a weld associated with welding of the inner barrier to an adjoining metal component of the impeller.
 35. The centrifugal pump according to claim 31 wherein the hermetic interconnection comprises a fusion associated with fusing of the inner barrier to an adjoining metallic component of the impeller. 